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Law enforcement officials said late Monday they found a bone fragment on the property next door to the home of Phillip Garrido, accused of keeping a then 11-year-old girl as his sex slave for nearly two decades and holding her hostage in his backyard.

Nearly two dozen officers spent the weekend combing the Antioch, Calif., property where Phillip Garrido and second wife Nancy Garrido hid Jaycee Dugard -- and the two children she eventually had with Phillip -- in a squalid compound of tents concealed by brush in their backyard for 18 years.

Authorities scoured Garrido's property and the immediate area with rakes, shovels and chain saws in the hopes of linking the couple to any other cases in the area. Cadaver dogs were unleashed in a yard of the couple's neighbor, where one of the suspects served as a caretaker.

A small bone fragment was found late Monday evening at the home of Garrido's neighbor, but cops said they weren't sure if the bone was human or animal.

The owner of the property is not a suspect, cops said.

The search came as Garrido's loved ones began speaking out about the accused kidnapper, saying they believe Garrido is a cold-blooded killer and "monster" capable not only of abducting Durgan -- but of murdering other women.

Manuel Garrido said he believes his son, Phillip, who stands accused of abducting Jaycee Dugard and fathering her two children, is involved in the slayings of other women, according the New York Post.

"He was a sex addict, that was his problem," his father told The Post. "I believe my son killed the prostitutes."

Garrido's first wife, Christine Murphy, told "Inside Edition" in an interview set to air Monday night that Phillip was a "monster" who "smacked" her around during their marriage -- and that he once tried to gouge her eyes out when Garrido attacked her in a jealous rage.

"I was always looking for a way to find out how to get away," she said. "He always told me he'd find me wherever."

Murphy said the Dugard case made her feel "sick to my stomach."

"He's capable of anything," she said of Garrido.

Garrido was previously convicted for kidnapping and raping Katie Callaway in 1976 after he asked Hall for a ride home from a supermarket in California, then bound and handcuffed her and took her to a warehouse. He served 10 years in prison of the 50-year sentence for the crime.

"Scream because my fears turned out to be justified -- he struck again," she said.

Phillip's victim, Dugard, now 29, was reunited with her mother, sister and another relative last Thursday. She is said to be in good health, but feeling guilty about developing a bond with Garrido, said her stepfather Carl Probyn. Her two children, Starlet and Angel, remain with her. The girls are aged 15 and 11.

"Jaycee has strong feelings with this guy. She really feels it's almost like a marriage," said Probyn, who was there when little Jaycee was snatched from a bus stop in 1991 and has been in contact with her mother since they found out the girl was alive.

"Hi, mom, I have babies," was Dugard's first words to her mother when they were reunited Thursday, Probyn said.

A team of psychiatrists have been with the family to help ease the transition -- which may be most difficult for Dugard's children, who just discovered that their father kidnapped their mother and held her against her will for nearly two decades.

"There's going to be a period of adjustment, no doubt, but they're doing very well at this point," FBI Special Agent Chris Campion said in an FBI podcast. "The two daughters are probably as happy as Jaycee is to be a part of this family."

The couple pleaded not guilty last Friday to 29 counts, including forcible abduction, rape and false imprisonment.

There were several close calls for rescue in the past. In 2006, neighbor Damon Robinson's then-girlfriend called police after she saw tents and children in the backyard. The responding officer failed to discover the encampment where authorities say Dugard was kept captive.

Police in Pittsburg are investigating whether Phillip Garrido, whose home is in nearby Antioch, is linked to several unsolved murders of prostitutes in the early 1990s. Antioch police are also looking into unsolved cases but declined further details.

Garrido seemed incoherent and mentally unstable, and the girls wore drab-colored dresses, were unusually subdued and had an unnaturally pale complexion, said Lisa Campbell, a special-events unit manager with UC Berkeley's police department.